JP2001324855A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the waste of toner constituting a patch being a toner image (patch) for detecting image density. SOLUTION: A magenta toner image (patch) 8M for detecting the image density is formed on a photoreceptor drum for magenta 11M by an image forming unit for magenta, and transferred to a transfer belt 30 rotating in a direction shown by arrow (b), and the density is detected by a density detection sensor 5. By applying a bias having the same polarity as the patch 8M to a transfer roller 15M by the transfer power source 71M of a voltage applying means 7M, the patch 8M after detecting the density is re-transferred to the drum 11M from the belt 30 and recovered by a cleaning device 14M so as to be utilized for the development of an electrostatic latent image. Other cyan, yellow and black patches are re-transferred to the photoreceptor drums for respective colors in the same manner.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic or electrostatic recording type image forming apparatus such as a copying machine or a printer.

[0002]

2. Description of the Related Art FIG. 8 shows a schematic configuration of a conventional image forming apparatus.

This image forming apparatus has a plurality of image forming units for speeding up multicolor image output, and successively multiplex-transfers toner images of different colors formed by these image forming units onto a recording material. Thus, a multicolor image is formed.

[0004] As shown in FIG.
The image forming apparatus includes image forming units M, C, Y, and Bk of four colors of magenta, cyan, yellow, and black, a transfer belt 30 as a transfer unit, and a fixing device 40 as a fixing unit.

Each of the image forming units M, C, Y, and Bk is
Photosensitive drum 11 that is an image carrier that rotates in the direction of arrow a
M, 11C, 11Y, and 11Bk, around which primary chargers 12M, 12C, 12Y, 12Bk,
Exposure devices 13M, 13C, 13Y, and 13Bk and developing devices 14M, 14C, 14Y, and 14Bk are provided.

The transfer belt 30 includes photosensitive drums 11M, 1
1C, 11Y, and 11Bk, are disposed in contact with each other, are stretched between a drive roller 31 and a separation roller 32, and are driven to rotate in the direction of arrow b.

The photosensitive drums 11M, 11C, 11Y, 11
The surface of Bk has primary chargers 12M, 12C, 12Y, 1
After being uniformly charged to a predetermined polarity and potential by 2Bk, an exposure device 13M, 13C, 13Y, 13Bk exposes an electrostatic latent image corresponding to a document image by exposure.
These electrostatic latent images are developed as toner images by attaching toner of each color by the developing devices 14M, 14C, 14Y, and 14Bk to which a developing bias is applied.

The recording material P fed by the feed roller 20
Is carried on the transfer belt 30 and sequentially conveyed to the transfer units of the image forming units M, C, Y, and Bk, and is transferred to transfer rollers (transfer members) 15M, 15C, 15Y, and 15Bk by transfer means ( Voltage applying means) 7M, 7C, 7Y, 7
By applying a transfer bias of a first polarity opposite to the polarity of the toner images on the photosensitive drums 15M, 15C, 15Y, and 15Bk by the transfer power supplies 72M, 72C, 72Y, and 72Bk of Bk, the toner images of each color are sequentially formed. Is transferred to and superimposed.

The recording material P after the transfer of the toner image is separated from the transfer belt 30 and conveyed to a fixing device 40, where the toner image is fixed on the surface thereof under pressure and heat.

On the other hand, the photosensitive drum 11 after the transfer of the toner image
For M, 11C, 11Y, and 11Bk, the toner remaining on the surface without being transferred to the recording material P (transfer residual toner) is removed by the cleaning devices 16M, 16C, 16Y, and 16Bk, and is used for the next image formation.

In the image forming apparatus shown in FIG. 8, toner remaining on the transfer belt 30 after separation of the recording material P (transfer residual toner) is a rubber blade, a fur brush, or a belt cleaner for a transfer belt using both of them. (Cleaning means)
It is scraped off by 33 and collected.

As shown in FIG. 9, an intermediate transfer member system is also known as a transfer system. An endless belt-shaped intermediate transfer belt (intermediate transfer body) 90 as a moving body that is wound around the rollers 101, 102, and 103 by applying the toner images of the respective colors formed by the image forming units M, C, Y, and Bk.
The primary transfer rollers 104M, 104C, 104Y, 1
The primary transfer is successively performed by 04Bk and superimposed, and the intermediate transfer belt 90 is rotated in the direction of the arrow b to move these toner images to the secondary transfer section having the secondary transfer roller 105. On the other hand, the recording material P is supplied to the secondary transfer section at a predetermined timing by the paper feed roller 20 or the like. Further, by applying a secondary transfer bias of a predetermined polarity to the secondary transfer roller 105, the toner images of each color on the intermediate transfer belt 90 are secondarily transferred onto the recording material P collectively. The toner images of each color transferred onto the recording material P are fixed by the fixing device 40.

In the image forming apparatus shown in FIG. 9, the toner remaining on the intermediate transfer belt 90 after the secondary transfer of the toner image (transfer residual toner) is a rubber blade, a fur brush, or an intermediate transfer belt using these in combination. Belt cleaner
(Cleaning means) It is scraped off by the 33 and collected.

In the image forming apparatus shown in FIGS. 8 and 9, a toner image (hereinafter referred to as a “patch”) for detecting image density ), A toner density of the patch is measured by a density detection sensor (density detection means) 5, and an image forming condition that satisfies an optimum image density is adjusted based on the result. To stabilize the image density.

[0015]

However, according to the above-mentioned conventional example, when a patch for image density detection is formed on the transfer belt 30 or the intermediate transfer belt 90 and density detection is performed, the patch is constructed. The toner (hereinafter referred to as “patch toner” as appropriate) is consumed without being used for image formation, and accordingly, the amount of toner actually used for image formation is reduced. During normal image formation, the transfer belt 30 or the intermediate transfer belt 90 is used.
The upper patch toner is not transferred to the recording material P,
Since all of them are removed and collected by the belt cleaner 33, the load on the belt cleaner 33 increases, cleaning efficiency decreases, and a large waste toner volume is required, and the frequency of replacing the waste toner container increases. Or

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides an image forming apparatus which does not waste toner constituting a toner image for detecting image density and reduces a load on a belt cleaner. It is intended to provide.

[0017]

According to a first aspect of the present invention, there is provided a toner image processing apparatus comprising: a plurality of image carriers arranged along a moving direction of a moving body; Forming a toner image on the plurality of image carriers by applying a voltage to a plurality of transfer members corresponding to each of the plurality of image carriers. In an image forming apparatus that sequentially transfers images onto a material, a first polarity opposite to a polarity of a toner image on the image carrier and a polarity of a toner image on the image carrier are applied to each of the transfer members. A plurality of voltage applying units each capable of applying the same second polarity, wherein each of the voltage applying units applies the voltage of the first polarity to the corresponding transfer member, whereby the image carrier Transferring the toner image on the body onto the moving body or the moving body The toner on the moving body is transferred onto an image carrier that forms a toner image of the same color as the toner by transferring the toner on the recording material and applying the second polarity voltage to the transfer member. Re-transfer.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, after being formed on each of the image carriers,
Density detecting means for detecting the density of the toner image for image density detection transferred onto the moving body, wherein the toner retransferred from the moving body to the image carrier is the toner for image density detection. The toner is a toner constituting an image.

According to a third aspect of the present invention, there is provided the first or second aspect.
In the above image forming apparatus, the image carrier is a photoconductor having a charge injection layer as an outermost layer.

The present invention according to claim 4 is based on claims 1, 2,
Or the image forming apparatus according to 3, further comprising charging means for charging the surface of the image carrier to a predetermined potential, wherein the charging means comprises:
A magnetic brush charger for injecting a charge into a charge injection layer provided on an outermost layer of the image carrier and charging the surface of the image carrier to a predetermined potential.

The present invention according to claim 5 is based on claims 1, 2,
In the image forming apparatus according to the third or fourth aspect, the moving body is a belt-shaped member formed endlessly.

According to a sixth aspect of the present invention, when the toner image for detecting the image density is opposed to an image carrier corresponding to the color of the toner image, In the image forming apparatus, a voltage of a second polarity is applied to the transfer member corresponding to the image carrier.

The present invention according to claim 7 is based on claims 1, 2,
In the image forming apparatus according to any one of 3, 4, 5, and 6, the image carrier that is located on the most downstream side and the image carrier that is located on the most upstream side along the moving direction of the moving body. And a charge applying means for applying a charge to the toner image on the moving body.

The present invention according to claim 8 is the invention according to claims 1, 2,
In the image forming apparatus according to any one of 3, 4, 5, 6, and 7, the image carrier located on the most downstream side and the image carrier located on the most upstream side along a moving direction of the moving body. A cleaning means for cleaning the surface of the moving body is provided between the body and the body.

According to a ninth aspect of the present invention, in the image forming apparatus of the eighth aspect, during the retransfer operation of the toner image on the moving body to the image carrier, the cleaning unit moves from the moving body. Being separated from each other.

[0026]

Embodiments of the present invention will be described below with reference to the drawings. 8 and 9 described above.
In FIGS. 1 to 7 referred to in the following description, members having the same configuration and operation will be denoted by the same reference numerals, and redundant description will be omitted as appropriate.

Embodiment 1 FIG. 1 shows an example of an image forming apparatus according to the present invention. The image forming apparatus shown in FIG.
Multi-color (color) in which a plurality of image forming units are arranged in order from the upstream along a moving direction (rotation direction) of a recording material carrier as a moving body that carries and conveys a recording material P such as paper as an image forming target. Image forming apparatus.

The image forming apparatus shown in FIG. 1 has a transfer belt 30 which rotates (moves) in the direction of arrow b as a recording material carrier.
And four image forming units M, C, Y, and Bk arranged in order from the upstream side to the downstream side along the rotation direction. In this order, magenta, cyan, yellow,
Each of them forms a black toner image. Each of the image forming units M, C, Y, and Bk is provided with a drum-type electrophotographic photosensitive member (hereinafter, referred to as a “photosensitive drum”) 11M, 11C, 11Y, and 11Bk as an image carrier. The photosensitive drums 11M, 11C, 11Y,
11Bk is rotationally driven at a predetermined process speed (peripheral speed) in the direction of arrow a by a driving means (not shown).

The photosensitive drums 11M, 11C, 11Y, 11
Around Bk, primary chargers (charging means) 12M, 12C, 12Y, and 12 that uniformly charge the surface of the photosensitive drum to a predetermined polarity and a predetermined potential substantially sequentially along the rotation direction.
Bk, exposure devices 13M, 13C, 13Y, 13Bk for exposing the charged photosensitive drum surface to form an electrostatic latent image, and attaching magenta, cyan,
Developing devices 14M, 14C, 14Y and 14Bk for developing as yellow and black toner images are provided.

The transfer belt 30 as a recording material carrier is
It is stretched over a driving roller 31 and a separation roller 32. The transfer belt 30 is rotated in the direction of arrow b by the rotation of the drive roller 31 with the recording material P such as paper conveyed by the paper feed roller 20 or the like carried on the surface. Inside the transfer belt 30, the transfer belt 30 is pressed against each of the photosensitive drums 11M, 11C, 11Y and 11Bk, and transfer rollers (transfer members) 15M, 15C, 1
5Y and 15Bk are provided.

Below the transfer belt 30, the transfer belt 3
A belt cleaner (cleaning means) 33 for cleaning the surface of the “0” is provided. The belt cleaner 33 is brought into contact with the surface of the transfer belt 30 by a contact / separation mechanism (not shown),
Also, they are configured to be separated.

A density detecting sensor (density detecting means) 5 is disposed at a position facing the driving roller 31 with the transfer belt 30 interposed therebetween. Here, assuming that the position on the transfer belt 30 where the recording material P is supplied is the most upstream side of the transfer belt 30, the density detection sensor 5
Image forming units M, C, Y,
That is, it is arranged further downstream than Bk.

In this embodiment, in order to further enhance the effect of the present invention, a distance of 100 mm is provided between two adjacent image forming units.

Hereinafter, the operation (image forming process) of the image forming apparatus having the above-described structure will be described, while appropriately describing the structure of each member. In the following, the process up to the transfer of the toner image will be described using the magenta image forming unit M as the first color as an example, but the same applies to the other image forming units C, Y, and Bk.

The photosensitive drum 11M as an image carrier has a cylindrical conductive metal base made of aluminum and having an outer diameter of 30 mm, and has a photo semiconductive layer, a charge transfer layer, a charge injection layer on its outer peripheral surface. Layers and the like are provided. Primary charger 12
As M, for example, a magnetic brush charger disclosed in JP-A-06-003921 is used, and charges are directly injected into the charge injection layer on the surface of the photosensitive drum 11M.

After a charging bias is applied by the primary charger 12M and the surface of the photosensitive drum 11M is uniformly charged to a predetermined polarity and potential (dark portion potential is -600 V),
Exposure is performed by the exposure device 13M, and the bright portion potential, which is the potential of the light-irradiated portion, is attenuated to -200 V, and an electrostatic latent image corresponding to the document image is formed.

The developing device 14M employs a contact developing method using a non-magnetic two-component developer containing carrier particles made of a magnetic material and a non-magnetic toner as main components. Carrier particles and toner particles are coated with a predetermined layer thickness in a negatively charged state on a developing sleeve made of stainless steel and having an outer diameter of 20 mm. The charge amount of the toner particles is about −30 μC / g for each color toner. The developing sleeve contains a predetermined magnetic pole and a magnet holding magnetic force. A DC voltage of -400 V and a peak-to-peak voltage Vpp of 2 k are applied to the developing sleeve at a predetermined timing.
A developing bias is applied in which an AC voltage of V and a frequency of 2 kHz is superimposed and applied. Thereby, the photosensitive drum 11
The electrostatic latent image on M is developed as a toner image with magenta toner attached.

The toner image formed on the photosensitive drum 11M is transferred by the transfer power supply 72M to a positive transfer bias (+100) having a first polarity opposite to the polarity of the toner image.
+1500 V) at a predetermined timing by the transfer roller 15M so as to synchronize with the toner image on the photosensitive drum 11M from the paper feed roller 20 to the transfer belt 3M.
The image is transferred to the recording material P supplied toward 0. At this time, toner (transfer residual toner) remaining on the surface of the photosensitive drum 11M without being transferred to the recording material P is described in Japanese Patent Application Laid-Open No. 9-096997.
As disclosed in Japanese Unexamined Patent Publication (Kokai) No. H07-205, a charge is applied by a primary charger (magnetic brush charger) 12M and recharged,
The toner is collected by the developing device 14M and then reused.

The above operation is also performed at predetermined timing in each of the cyan, yellow, and black image forming units C, Y, and Bk other than the magenta image forming unit M, and is formed on each of the photosensitive drums 11C, 11Y, and 11Bk. The toner images of the respective colors are sequentially transferred so as to be superimposed on the magenta toner images already transferred on the recording material P held on the transfer belt 30.

The recording material P on which the toner image has been transferred is supplied to the fixing device 40 by the transfer belt 30 and heated (about 1
90.degree. C.) and pressure (total pressure 40 kg) to fix the toner image on the surface, thereby obtaining a full-color image.

The surface of the transfer belt 30 that has finished supplying the recording material P to the fixing device 40 is cleaned by a belt cleaner 33.

The density control is performed at a timing different from the above-described image forming step. As a method therefor, a patch (toner image for density detection) is formed on the transfer belt 30, and the toner density is detected by the density detection sensor 5.
This is to optimize image forming conditions based on the detection result.

The steps up to the formation of the patch on the transfer belt 30 are performed in the same manner as the above-described image forming step. However, the recording material P is not fed by the feed roller 20 only during the density control. Therefore, the patch is formed directly on the transfer belt 30.

In this embodiment, a plurality of patches for each color are formed in order from the downstream side in the moving direction of the transfer belt 30a, that is, black → yellow → cyan → magenta, and the image forming conditions are determined based on the detected density data. Feedback. Specifically, the image forming conditions to be fed back include charging bias, developing bias, transfer bias, laser pulse width modulation of an exposure device, and the like.

For the purpose of simplifying the present invention, the patch formation area is adjacent to each other for each color.
An area of 100 mm or less, which is the distance between individual image forming units, is provided. In the present embodiment, in order to stabilize the detection accuracy of the patch density and the density control, the number of patches formed for each color is four, and the size of the patch is a square having a side of 20 mm.

This embodiment is characterized in that patches for density detection formed on the transfer belt 30 are collected again by the same color image forming unit. The patch for density detection is collected in the following procedure.

The first color magenta will be described with reference to FIG.

At the time of density control, the magenta patch 8M formed on the transfer belt 30 is charged to a negative polarity, and is conveyed to the place where the density detection sensor 5 is disposed with the movement of the transfer belt 30. Is done.

After the toner density of the patch 8M is detected by the density detection sensor 5, the patch 8M is transported to the image forming unit M again. At the time of the density control, the belt cleaner 33 is kept until the patch 8M is conveyed to the belt cleaner 33.
Are on standby in a state separated from the transfer belt 30.

In synchronization with the timing when the patch 8M is again conveyed to the image forming unit M, as shown in FIG. 3, the transfer power supply 72M is switched to the transfer power supply 71M.
A transfer bias (−100 to −1500 V) of a negative polarity (second polarity) having the same polarity as the charging polarity of the toner forming the patch 8 </ b> M on the transfer roller 15 </ b> M is applied for a time corresponding to the magenta patch forming region section. Only apply. The patch 8M on the transfer belt 30 to which the transfer bias of the same polarity is applied by the transfer power supply 71M is re-transferred onto the photosensitive drum 11M to receive a repulsive electrostatic force.

The toner (re-transferred toner) returned to the photosensitive drum 11M is provided with a predetermined toner tribo by the primary charger 12M and collected by the developing device 14M as disclosed in JP-A-09-096997. Thereafter, the toner image is reused for developing the toner image on the photosensitive drum 11M. When the recovery rate of the toner constituting the patch 8M was verified under the above conditions, 98% of the toner was recovered.

The same operation as that for the magenta patch 8M is performed for other color patches, that is, cyan, yellow, and black patches 8C, 8Y, and 8Bk. Is collected in the image forming unit of that color.

Further, patches 8M, 8C, 8Y,
8Bk of toner is applied to the photosensitive drums 11M, 11C, 1
The toner remaining on the transfer belt 30 after being collected on 1Y, 11Bk (recovered toner) is conveyed to the belt cleaner 33 as shown in FIG. 4 as the transfer belt 30 rotates in the direction of the arrow b. Recovered toner is belt cleaner 3
The belt cleaner 33 that has been waiting in a state of being separated from the transfer belt 30 immediately before being conveyed to the transfer belt 30 is brought into contact with the transfer belt 30 by a driving device (not shown), and the remaining toner on the transfer belt 30 is recovered. Is removed. in this case,
Since the amount of the residual toner to be collected is extremely small, reliable cleaning is performed, and the problem of insufficient cleaning does not occur.

Next, an evaluation result based on this embodiment will be described.

In the image forming apparatus having the above-described configuration, (density control + transfer belt cleaning for one round of the transfer belt), that is, this set was repeated with a total of two rounds of the transfer belt 30 as one set.

The evaluation items were (1) measurement of the amount (weight) of toner accumulated in the belt cleaner 33, and (2) cleaning property of the transfer belt 30. The number of times the density control was repeatedly executed was 100 times.

First, as a comparison, it was confirmed that patches for density detection were not collected in the image forming unit.

By controlling the concentration 100 times, about 5 g
Has been accumulated in the belt cleaner 33. In addition, poor cleaning has occurred, in which the density detection patch remains on the transfer belt 30 without being sufficiently cleaned.

On the other hand, when the patch for density detection is collected in the image forming unit of the own color, the amount of toner accumulated in the belt cleaner 33 is 0.1 g or less, and the patch toner is hardly formed in the image forming unit. It was confirmed that it was collected by the unit.

Further, one of the transfer belts 30 after the density control is performed.
Remaining toner on the transfer belt 30 can hardly be confirmed only by cleaning the circumference, and the load on the belt cleaner 33 can be reduced by collecting the density detection patch in each image forming unit. It was also confirmed that the cleaning efficiency was sufficiently improved.

In this embodiment, as shown in FIG. 5, the order of density detection patches is black → yellow → cyan → magenta with respect to the moving direction of the transfer belt 30. By setting the patch formation area to be equal to or less than the distance between the image forming units, it becomes possible to apply the transfer bias applied when collecting the image forming units to all the colors simultaneously, thereby simplifying the collection process. Became possible.

However, the order of forming the patches for each color is not limited to this. Therefore, a case where the order of forming the patches for each color is different from magenta → cyan → yellow → black will be described with reference to FIG.

This means that the density detection patch is formed from magenta located on the most upstream side when viewed from the moving direction of the transfer belt 30 of the image forming unit. With this configuration, the magenta density detection patch 8M formed at the forefront on the transfer belt 30 is
After the rotation of the magenta image forming unit M, the magenta transfer roller 15M is transferred to the magenta transfer roller 15M by the transfer power supply 71M in synchronization with the timing at which the magenta patch 8M contacts the magenta image forming unit M. A transfer bias (−100 to −1500 V) is applied, and the toner of the magenta patch 8M is collected in the image forming unit M. When the magenta toner is collected, no transfer bias is applied to the other transfer rollers 15C, 15Y, and 15Bk.

Thereafter, the patch 8C for detecting the density of cyan which has passed through the transfer section of the magenta image forming unit M is collected in the cyan image forming unit C, and similarly, the image forming units Y are sequentially arranged in the order of yellow and black. , B
k collects patches 8Y and 8Bk for density detection.

With this method, it is not necessary to limit the number of patches of each color in the patch formation area of each color.

The configuration of the transfer belt 30 has the same effect even when an intermediate transfer member is used. Therefore, either a multicolor image forming apparatus in which a plurality of image forming units are arranged in parallel with the transfer belt 30 or a multicolor image forming apparatus in which a plurality of image forming units are arranged in parallel with the intermediate transfer belt (intermediate transfer body). Accordingly, the present invention is effective, and it is possible to suppress the consumption of toner and to increase the cleaning efficiency of the transfer belt or the intermediate transfer belt.

As described above, in a multicolor image forming apparatus which performs density control by forming a patch for density detection on a transfer belt or an intermediate transfer belt, the patch toner of each color is again applied to an image forming unit of the same color. By letting you collect,
The toner consumption can be reduced, and the cleaning efficiency of the belt cleaner 33 can be further improved.

<Embodiment 2> FIG. 7 is a schematic configuration diagram of an image forming apparatus according to Embodiment 2 of the present invention. In the second embodiment, the charge applying means 6 is added to the multicolor image forming apparatus having the transfer belt 30 described in the first embodiment. The charge applying means 6 is arranged downstream of the image forming unit Bk on the most downstream side so as to face the surface of the transfer belt 30 with a predetermined gap therebetween.
The charge applying means 6 applies an electric charge to the patch for density detection formed on the transfer belt 30 until the patch is conveyed to the image forming unit again, so that the transfer belt 30
The upper patch has a predetermined charge amount.

As the charge applying means 6, a corona charger can be used.
DC voltage at a peak-to-peak voltage of 10 kVpp and a frequency of 50 kVpp.
A bias on which an AC voltage of 0 Hz is superimposed is applied.
The reason for superimposing the DC voltage and the AC voltage is that the transfer belt 30
This is for uniformly giving a tribo to all of the above toners.

The purpose of providing the charge applying means 6 is to further improve the efficiency of collecting the patch toner on the transfer belt 30 to the photosensitive drum. That is, the toner tribo is approximately −30 μC / g in a normal state, but the toner tribo may generally gradually decrease depending on the use condition and use environment of the developing device. With a tendency.

In general, the toner tribo tends to decrease in accordance with the use condition, and the tribo tends to be high in a low humidity environment and low in a high humidity environment.

The purpose of the charge applying means 6 is to increase the toner tribo of the patch for density detection in order to improve the collection efficiency especially when the toner tribo is lowered. That is, the transfer power source 7 having the same polarity as the toner polarity
Since the toner is collected on the photosensitive drums 11M, 11C, 11Y, and 11Bk by the repulsive electrostatic force of 1M, 71C, 71Y, and 71Bk, when the toner tribo is low, the photosensitive drums 11M, 11C, 11Y, and 11B
This is to avoid a problem that the toner is not sufficiently collected in k.

When the same evaluation as in Embodiment 1 was performed with the above configuration, no reduction in the toner consumption rate was observed, and no problem was found in cleaning the transfer belt 30. Further, the effects of the present invention were confirmed regardless of the use frequency and use environment of the multicolor image forming apparatus.

The intermediate transfer belt system can be used, and the position of the charge applying means 6 is not limited to the position described above.

According to the second embodiment, the charge applying means 6
By controlling the toner tribo of the patch for density detection by the charge applying means 6, the collection efficiency of the patch for density detection to the image forming unit is also stabilized, and the occurrence of cleaning failure of the transfer belt or the intermediate transfer belt is reduced. It became possible to avoid.

[0076]

As described above, according to the present invention,
By collecting the unnecessary toner on the moving body by the image carrier corresponding to the color of the toner, the toner can be reused. Further, a new mechanism for removing unnecessary toner on the moving body is not required, and the burden on the cleaning means for removing unnecessary toner on the moving body can be reduced.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view illustrating a schematic configuration of an image forming apparatus according to a first embodiment.

FIG. 2 is a longitudinal sectional view showing an arrangement position and operation of a density detection sensor according to the first embodiment.

FIG. 3 is a diagram illustrating an operation at the time of collecting a toner image (patch) for detecting image density according to the first embodiment.

FIG. 4 is a diagram illustrating the operation of a belt cleaner (cleaning means) according to the first embodiment.

FIG. 5 is a diagram illustrating an example of a method of forming a toner image (patch) for detecting image density according to the first embodiment.

FIG. 6 is a diagram illustrating another method of forming a toner image (patch) for detecting image density according to the first embodiment.

FIG. 7 is a diagram illustrating an arrangement position of a charge applying unit in Embodiment 2.

FIG. 8 is a longitudinal sectional view showing a schematic configuration of a conventional image forming apparatus using a transfer belt (recording material carrier).

FIG. 9 is a longitudinal sectional view showing a schematic configuration of a conventional image forming apparatus using an intermediate transfer belt (intermediate transfer belt).

[Explanation of symbols]

5 Density detecting means (density detecting sensor) 6 Charge applying means 7M, 7C, 7Y, 7Bk Voltage applying means (transfer means) 8M, 8C, 8Y, 8Bk Toner images (patches) 11M, 11C, 11Y for image density detection 11Bk Image carrier (photosensitive drum) 12M, 12C, 12Y, 12Bk Charging means (primary charger, magnetic brush charger) 15M, 15C, 15Y, 15Bk Transfer member (transfer roller) 30 Moving body (recording material carrier, (Transfer belt) 33 Cleaning means (belt cleaner) 71M, 71C, 71Y, 71Bk, 72M, 72C,
72Y, 72Bk transfer power supply 90 Moving body (intermediate transfer body, intermediate transfer belt) P Recording material

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H003 BB11 CC04 2H005 AA21 CA21 DA01 DA07 FC01 2H030 AB02 AD03 BB23 BB36 BB54 2H032 AA05 AA15 BA18 BA27 BA30 CA01 CA15 2H068 AA01 FB13 FC01 FC08 FC11 FC15

Claims (9)

[Claims] A plurality of image bearing members arranged along a moving direction of the moving member to form toner images of different colors on each of the plurality of image bearing members;
By applying a voltage to a plurality of transfer members corresponding to each of the plurality of image carriers, the toner images on the plurality of image carriers are sequentially placed on the moving body or a recording material carried on the moving body. In the image forming apparatus, for each of the transfer members, a first polarity opposite to a polarity of the toner image on the image carrier and a second polarity same as the polarity of the toner image on the image carrier are provided. And a plurality of voltage applying units each of which can apply a polarity of the first polarity to the corresponding transfer member by applying a voltage of the first polarity to the corresponding transfer member. An image is transferred onto the moving body or onto a recording material carried by the moving body, and a voltage of the second polarity is applied to the transfer member, so that the toner on the moving body has the same color as the toner. On the image carrier that forms a toner image of Transfer to the image forming apparatus characterized by. 2. A method for detecting the density of a toner image for image density detection, which is formed on each of the image carriers and then transferred onto the moving body, comprises: The image forming apparatus according to claim 1, wherein the toner retransferred to the carrier is a toner constituting the toner image for detecting the image density. 3. The image forming apparatus according to claim 1, wherein the image carrier is a photoconductor having a charge injection layer as an outermost layer. 4. A charging device for charging the surface of the image carrier to a predetermined potential, wherein the charging device injects a charge into a charge injection layer provided on an outermost layer of the image carrier to form the image. The image forming apparatus according to claim 1, wherein the image forming apparatus is a magnetic brush charger that charges a surface of the carrier to a predetermined potential. 5. The image forming apparatus according to claim 1, wherein the movable body is a belt-shaped member formed endlessly. 6. When the toner image for image density detection faces an image carrier corresponding to the color of the toner image, a voltage of a second polarity is applied to the transfer member corresponding to the image carrier. The image forming apparatus according to claim 2, wherein a voltage is applied. 7. The image forming apparatus according to claim 1, further comprising: a space between the image carrier located at the most downstream side and the image carrier located at the most upstream side along the moving direction of the movable body. The image forming apparatus according to claim 1, further comprising a charge applying unit that applies a charge to the toner image. 8. The surface of the moving body between the image carrier located on the most downstream side and the image carrier located on the most upstream side along the moving direction of the moving body. The image forming apparatus according to claim 1, further comprising a cleaning unit configured to perform cleaning. 9. The cleaning device according to claim 8, wherein the cleaning unit is separated from the moving body during a retransfer operation of the toner image on the moving body to the image carrier. Image forming device.